The present invention relates to a method for manufacturing a liquid crystal display device which is used in an optical display, and more particularly to a method for forming an insulation layer to partition liquid crystal layers in a liquid crystal display having a multi-layer liquid crystal structure.
Currently utilized liquid crystal display devices, of an active matrix type use a simple X-Y matrix or thin film transistor (TFT) driving method both driving methods use a twisted nematic (TN) type or super twisted nematic (STN) type liquid crystal and a polarizing plate for controlling light. However, the polarizing plate in the liquid crystal display (LCD) intercepts more than 50% of the light. Accordingly, efficiency is lowered. For this reason, a background light source having a considerable intensity is required to obtain a picture image having a desired brightness. Thus, in a laptop word processors or computers which use a dry cell battery or an accumulative battery cell as a power supply source extended use is limited due to the excessive power consumption of the light source.
Also, in known LCDs, including the TN and STN LCD devices, since the liquid crystal is charged between two glass plates, a cell gap must be made within stringent range requirements to form a uniform picture image. Therefore, due to current technological limitations in the manufacturing of glass plates, enlarging LCD panels is hard to achieve.
Taking the above-described problems into consideration, in order to decrease the need for very precise cell gap adjustment, it has been known to eliminate the polarized plate to increase efficiency and instead use a single sheet of a base plate. Examples of LCD without a polarized plate include a cholesteric nematic transition (CNT) type which uses a phase transition effect and a dynamic scattering mode (DSM) type which was devised early in LCD development. The DSM type LCD exhibits slow response time and cannot be made thin. For those reasons it is no longer in common use.
Another example of an LCD not using a polarized plate to increase the efficiency of light is a polymer-dispersed liquid crystal display (PDLCD). However, since the PDLCD is made of a polymer material, more than half of whose volume is light-transmitting, the scattering of light is needed to obtain a clear contrast ratio. To attain these requirements, there is structural limitation that the thickness of the liquid crystal layer should be at least 20 m.
An LCD which adopts an electrical field effect type liquid crystal having a new structure, in which the above conventional LCD problems are considerably improved, if the parent application to this continuation-in-part application, which bears U.S. patent application Ser. No. 08/058,712, was filed on May 10, 1993, and is expressly incorporated by reference herein.
The LCD described the parent application Ser. No. 08/058,712 has a fast driving speed and a high light-utilization efficiency. Liquid crystal layer provided between the opposing electrodes is isolated by a plurality of insulation layers to form a multi-layer structure. A polarized plate is not used and only a single sheet of a glass substrate is applied. As shown in FIG. 1, liquid crystal layers 20 of the electrical field effect type are provided between opposing electrodes 10 and 18. The thickness of each liquid crystal layers 20 is maintained by the columns 12. Insulation layers 22 for separating each liquid crystal layer 20 are provided between adjacent liquid crystal layers 20. The mutual location of insulation layers 22 is fixed by columns 12 which are provided locally. Injection holes 14 for locally injecting the liquid crystal are provided on one side of the insulation layer 22. Here, the thickness of each liquid crystal layer is less than or equal to 3 m. The thickness of each layer of the insulation layer is preferably less than or equal to 5 m. The insulation layer 22 can be made of an epoxy resin material, or a metal oxide, particularly an aluminum oxide.
FIG. 2 illustrates a top view of LCD, and, in particular, the arrangement of column 12 and injection holes 14 in relation to an electrode 10. FIGS. 3 and 4, illustrate the A--A and B--B cross sectional views of this LCD, respectively.
The manufacturing sequence of the above described reflective-type LCD by the above method will be described with reference to FIG. 5-10.
In FIG.5, an electrode 18 of a predetermined pattern is formed of a conductive material on black plastic substrate 16.
In FIG. 6, epoxy resin layer 20 and PVA layer 22a are alternately laminated a number of times on electrode 18 of FIG. 5, by a spin coating or roll coating method. Then, an upper electrode 10 is formed of indium tin oxide (ITO) on epoxy resin layer 20.
In FIG. 7, a photo mask pattern is formed on the surface of the uppermost epoxy resin layer, leaving a photoresist 24 as shown in FIG. 7.
The portion not covered by photoresist 24 is plasma-etched to form a hole for column 12. Then, the hole is filled with the epoxy resin. At the same time, the epoxy resin is coated on the exposed surface to form column 12 and surface epoxy resin layer 26. Thereafter, a shielding plate 11 is formed over each column 12.
In FIG. 8, liquid crystal inlet holes 14 are formed by photo mask patterning and plasma etching. Thereafter, water, acetone or alcohol is injected via inlet hole to thereby dissolve and remove each PVA layer 22a. Accordingly, inlet holes 14 and each portion 22b are left empty. Each epoxy resin layer 20 is supported by column 12 to sustain each liquid crystal layer portion space 22b.
In FIG. 9, after the resultant structure is dried, liquid crystal is coated on the whole upper surface thereof under a vacuum to fill each inlet hole 14 and evacuated portion 22b to form a liquid crystal layers 22. Thereafter, as shown in FIG. 10, an epoxy resin is coated on the whole surface to seal the liquid crystal inlet hole 14, and shielding plate 11 is formed directly above each column 12 and inlet hole 14 which require the light to be shielded. Accordingly, the reflective-type LCD shown in FIGS. 1 through 4 results. It should be noted that the shielding plate is not shown in FIGS. 1 through 4.
In the above described manufacturing method, water-soluble PVA is used as a dissolution layer, and epoxy resin is used as an insulation layer. However, the materials employed here are not limited to these. For instance, it is suggested that a metal such as aluminum can be used instead of the water-soluble PVA, and that a metal oxide can be used instead of the epoxy resin. The drawbacks of this method are (1) that the dissolution of the dissolution layer cannot be completed in a short time and (2) a portion of the insulation layers and columns may be damaged during the dissolution process. However, the dissolution time cannot be reduced significantly. Furthermore, when the dissolution layer and the insulation layer are comprised of a metal and a resin, respectively, internal stresses are caused between the two materials because of the different thermal expansion ratios thereof, which can cause undesirable cracking.